Thursday's report into the appalling cover-up by the church and public officials of abuse by Catholic priests in the archdiocese of Dublin is as detailed, and unsparing, as the previous one in May into physical brutality in Ireland's church-run reform schools. Almost no one emerges unscathed. Abusive priests were shuffled around by bishops; the police force and judges looked the other way, or left it to the bishops; canon lawyers ignored canon law. Children were silenced, and sacrificed on the altars of respectability. The levels of arrogance and denial are bewildering. The purgation is massive. Just as the church begins Advent, Ireland is plunged into Lent.

The charge laid at the church's door is simple and devastating. From the 1960s through to the 1990s, none of the four archbishops of Dublin reported the abuse that was brought to their attention: as the report says, "The Dublin archdiocese's pre-occupations in dealing with cases of child sexual abuse, at least until the mid 1990s, were the maintenance of secrecy, the avoidance of scandal, the protection of the reputation of the church, and the preservation of its assets. All other considerations, including the welfare of children and justice for victims, were subordinated to these priorities. The archdiocese did not implement its own canon law rules and did its best to avoid any application of the law of the state."

It takes great courage for a society to untangle webs of corruption and complicity, to lay the blame fairly and squarely where it should fall, and to do so without reaching for scapegoats. The Murphy Commission, like the Ryan Commission before it, took years, and involved an army of academics and judicial investigators. Appalling, sickening, revolting, shameful: the adjectives to describe the cover-up of clerical sexual abuse is as endless, and as inadequate, as the inevitably stuttering attempts by today's bishops and public officials to apologise for it. But there is only one real apology that matters: financial compensation in recognition of the harm caused, and a new mindset – yes, and rules – that ensure it cannot happen again.

That shift has long since occurred. The reason this report can take place at all is because the church has accepted its complicity and handed over its files. New rules prevent any attempt to put other considerations before the welfare of the minor; there is no way now that the church can deal with abuse in an internal forum instead of an external, public forum.

But an important point has been lost in the coverage. The Irish Times leads the way in claiming that the church dealt with abuse allegations using canon law instead of civil law: "Canon law, which favours abusers over abused, has contributed in a malign way," it claims. But canon law does not favour the abuser, and the Murphy report does not condemn its provisions as inadequate. It notes that since time immemorial child sexual abuse has been both a grave sin and a serious crime in canon law.

As the report points out, the 1917 code of canon law – which was valid until the new code of 1983 (which did not change this) – "decreed deprivation of office and/or benefice, or expulsion from the clerical state for such offences." A bishop who hears of an allegation of abuse has the obligation in canon law to investigate it, and if it is true, to subject the priest to trial and expel him from the priesthood. That is what must happen independently of, and parallel to, investigation and prosecution by the civil authorities.

But that is not what happened. Chapter 4 of the report documents a "collapse of respect for canon law in archdiocesan circles ... offenders were neither prosecuted nor made accountable within the church". Only two canonical trials ever took place in the 30-year period under investigation, both in the 1990s and in the teeth of the opposition of one of the most powerful canonists in the archdiocese, Mgr Sheehy, who "actually considered that the penal aspects of that law should rarely be invoked".

There has never been any doubt, in the Catholic church, of the wrongness of child sex abuse, and its own law reflects this. It is scandalous, of course, that the church ignored the civil law; but as the report shows, for decades civil law in Ireland was severely lacking in its will and capacity to prosecuted clerical abusers. The real scandal is that the church ignored its own law, derived from explicit and unambiguous biblical teaching, a law valid for the church in all political and legal contexts around the world. The principle in canon law is clear and unambiguous: whatever the inadequacies of the civil law, minors must always be protected by the church's law, and their abusers brought swiftly to justice. The failure to obey its own law over many decades in the archdiocese of Dublin, as in other dioceses in the US and the UK, will haunt the church for years to come.